1. Field of the Invention
This invention relates to a process for removal of suspended solids and adsorbable contaminants from an influent liquid containing same.
2. Description of the Prior Art
In the field of liquid and wastewater treatment, filtration has long been a major method of removing suspended solids from liquid streams. In wastewater treatment applications in particular, the presence of suspended solids materials is frequently a major process problem and filtration has commonly been employed as a means of reducing and/or removing suspended solids from streams such as municipal sewage and wastewater intended for recycle use. In such applications, downflow and upflow sand filters and dual or mixed media filters have been widely employed and have in general been shown to be cost effective and efficient in use. Nonetheless, work by practitioners in the field has shown that sand and mixed media filters are in general effective in removing suspended solids, but only under limited solids loading conditions. In general, solids concentrations of the liquid stream entering the filter must be below about 100-200 milligrams/liter. At suspended solids concentration values above this level, the filtration bed is susceptible to clogging and high pressure drop across the bed.
In recent years, the operation of filtration has been somewhat improved in the foregoing applications by the use of polyurethane as a filtration medium. In general practice, polyurethane foam is cut up into small pieces and placed into a retaining vessel to form the filtration bed. Wastewater or other liquid containing suspended solids is then flowed through the bed with resulting deposition of suspended solids on the polyurethane particles. The suspended solids thus remain on the polyurethane particles and the liquid from which the suspended solids has been deposited subsequently passes through the bed and is discharged as liquid depleted in suspended solids.
In general, the use of polyurethane foam as a filtration medium provides numerous operating advantages over beds employing sand or conventional mixed media filtration materials, including higher solids capacity, lower pressure drop head losses, higher resistance to clogging and removal of numerous soluble organic contaminants from the liquid stream.
For removal of adsorbable contaminants, such as toxic organic chemical species, from liquid, it has been common practice in the liquid treatment field to employ adsorbent beds through which the liquid containing adsorbable contaminants is passed for removal of such contaminants. In particular, activated carbon has been widely employed as an adsorbent medium due its high selectivity for many organic and inorganic contaminants of liquid streams. In the field of wastewater treatment, such adsorbers are generally quite large in size, involving 30-60 minute adsorbent bed liquid retention times. The liquid undergoing treatment requires prior filtration in order to avoid clogging of the adsorbent bed, and the adsorbent usage rate has to be substantial before on-site regeneration renders the adsorbent costs economical, e.g., activated carbon usage must generally be greater than about 600 pounds per day before on-site regeneration renders the activated carbon adsorbent costs reasonable on a per-pound basis.
To overcome the requirement of prior filtration up-stream of the adsorbent bed, the prior art has proposed to operate the adsorbent bed in an expanded or fluidized bed operating mode. Such mode of operation has utility primarily for treatment of liquids with low solids levels, e.g., less than 100 milligrams suspended solids per liter, while higher solids content liquid streams are likely to still require filtration, and even in low solids content liquid treatment operation where expanded or fluidized bed operation is possible, the liquid effluent from the adsorbent bed will still contain substantial levels of suspended solids.
The prior art has further proposed to employ powdered adsorbents for removal of adsorbable contaminants from liquid in wastewater treatment by the activated sludge process, by adding the powdered adsorbent, such as activated carbon, directly to the wastewater treatment aeration tank. In such modifications, the powdered activated carbon or other adsorbent is mixed with the biological activated sludge solids and, as a result, both the adsorbent and the biological solids have to be dewatered and regenerated together, which is disadvantageous from the standpoint of operating system complexity and treatment cost. Furthermore, such modification results in only slight polishing, i.e., removal of adsorbable contaminants, from the treated liquid.
Accordingly, it is an object of the invention to provide an improved, integrated process for treatment of suspended solids--and adsorbable contaminant--containing liquid, by filtration with porous polyurethane particles and sorbable contaminant removal with particulate adsorbent.
Other objects and advantages of the invention will be apparent from the ensuing disclosure and appended claims.